A power supply control device described in JP 2007-295699 A outputs power supplied from a direct current power source (hereinafter referred to as a DC power supply), which is connected to an input side, via a transformer. The power supply control device described in JP 2007-295699 A (corresponding to US 2009/0108674 A1) includes a main electrical power storage device, a capacity load connected between power lines of the main electrical power storage device, and an auxiliary electrical power storage device connected between the power lines of the main electrical power storage device in parallel with the capacity load via a two-way converter. Power is exchanged between the main electrical power storage device and the auxiliary electrical power storage device with the use of the two-way converter. By supplying power of the auxiliary electrical power storage device to the capacity load using the two-way converter, the capacity load is charged until a voltage across the capacity load becomes equal to a voltage across the main electrical power storage device.
When the two-way converter in the power supply control device described in JP 2007-295699 A includes a choke coil on the auxiliary electrical power storage device side, the capacity load is charged by an increase and decrease of a current repetitively flowing through the choke coil. The power supply control device described in JP 2007-295699 A does not include a current limiting resistor or the like used to prevent an inrush current for reducing system cost and system size.
A current flowing through the choke coil decreases under a condition that a voltage across the auxiliary electrical power storage device is smaller than a value found by dividing a voltage across the capacity load by a turn ratio of coils. Herein, the coils are provided as the two-way converter. Hence, in a case where a voltage across the capacity load is small at the beginning of a charging operation, a current flowing through the choke coil continues to increase. As a result, a DC-to-DC converter may eventually deteriorate or break. On the other hand, by turning off switching elements to decrease a current flowing through the choke coil, a counter-electromotive force is induced by an avalanche current, and the switching elements may possibly deteriorate or break.